No. 109.] 113 



Strophomena (Stropiiodonta) hemisfherica (n. s.). 



Pal. N.Y. Vol. IT. 



Shell subcircular or semicircular ; hinge crenulated, nearly or 

 quite equal to the greatest width of the shell, terminating in 

 small distinct ears : dorsal valve extremely gibbous, almost 

 hemispherical : ventral valve concave, sometimes geniculated 

 on the front and lateral margins ; dental apophyses prominent, 

 and extending beyond the hinge-line. Surface marked by fine, 

 closely arranged radiating strise ; about every fourth, fifth, or 

 sixth one of which is a little larger than the others : extremely 

 fine, nearly obsolete concentric strise mark the surface in the 

 other direction : sometimes very small indistinct concentric 

 wrinkles are visible, especially in the umbonal region. Interior 

 of the shell granulose. 

 Geological position and locality. Corniferous limestone, N.Y., and in 



the same rock at the falls of the Ohio, and at many other western localities. 



Strophomena ( Strophodonta) inequiradiata (n. s.). 



Pal. N.Y. Vol. iy. 



Shell nearly semicircular ; length about two-thirds the breadth ; 

 hinge-line crenulated, equalling the greatest width of the shell : 

 dorsal valve concave, distinctly incurved near the hinge : ven- 

 tral valve convex, forming a distinct arch from beak to front, 

 sloping to the sides ; beak and area strongly incurved. Surface 

 marked by somewhat coarse distant radiating strise, which in- 

 crease by interstitial addition : the spaces between these larger 

 strioe are occupied by extremely fine closely arranged parallel 

 lines, which are crossed by finer, regular, close concentric striss, 

 so as to present, under a good magnifier, a delicate cancellate 

 surface. Interior finely granulose ; granules arranged in irregu- 

 lar radiating row^s. 

 This species is closely related to LeptcBna haueri of Barrande (Brach. 



aus Bohm ; Haidinger, Naturwissenschaftliche Abhandlungen, pa. 242, 

 [Senate No. 109.] 8 



